Method and system for providing feedback data useful in prosthodontic procedures associated with the intra oral cavity

ABSTRACT

Feedback data useful in prosthodontic procedures associated with the intra oral cavity is provided. First, a 3D numerical model of the target zone in the intra oral cavity is provided, and this is manipulated so as to extract particular data that may be useful in a particular procedure, for example data relating to the finish line or to the shape and size of a preparation. The relationship between this data and the procedure is then determined, for example the clearance between the preparation and the intended crown. Feedback data, indicative of this relationship, is then generated, for example whether the preparation geometry is adequate for the particular type of prosthesis.

This application claims the benefit of prior U.S. provisional patentapplication No. 60/630,572 filed Nov. 26, 2004, the contents of whichare hereby incorporated by reference in their entirety.

FIELD OF THE INVENTION

This invention relates to a system and method for providing feedbackinformation that facilitates and that may provide guidance forprosthodontic procedures in the intra oral cavity, i.e., proceduresinvolving the installation and definition of dental prostheses. Inparticular, the invention relates to such systems and methods that arecomputerized.

BACKGROUND OF THE INVENTION

Prosthodontics is the dental speciality concerned with artificialreplacements of missing parts of the mouth and jaws, in particular ofteeth and parts thereof.

In prosthodontic procedures designed to implant a dental prosthesis inthe intra oral cavity, the dental site at which the prosthesis is to beimplanted in many cases needs to be measured accurately and studiedcarefully, so that a prosthesis such as a crown or bridge, for example,can be properly designed and dimensioned to fit in place. A good fit isof the highest importance to enable mechanical stresses to be properlytransmitted between the prosthesis and the jaw, and to prevent infectionof the gums and so on via the interface between the prosthesis and thedental site.

In the prior art, the dental site is prepared by the dentalpractitioner, and a positive model of the site is constructed usingknown methods. Alternatively, the dental site may be scanned to provide3D data of the site. In either case, the virtual or real model of thesite is sent to the dental lab, which manufactures the prosthesis basedon the model. However, if the model is deficient or undefined in certainareas, or if the preparation is not optimal for receiving theprosthesis, the dental technician has a more difficult job ahead thanotherwise, and may result in less than optimal design for theprosthesis. In some circumstances, the model is rejected and the dentalpractitioner must re-scan the dental site, or must rework thepreparation, so that a suitable prosthesis may be produced.

SUMMARY OF THE INVENTION

Herein, “dental material” refers to any material associated with dentalstructures of the intra oral cavity, including but limited to naturaldental materials such as for example enamel, dentine, pulp, dentalroots, and non-natural dental materials such as for example metallic andnon-metallic filings, restorations, crowns, bridges, copings,preparations, and so on.

Herein, “dental clinic” refers to the interface between a dentalpractitioner and a patent, and thus includes any physical entity, inparticular a clinic, in which there is interaction between a dentalpatient and a dental practitioner. While “dental practitioner” typicallyrefers to a dentist, doctor or dental technician, it also includesherein all other caregivers that may interact with a dental patientduring the course of a dental treatment. While “dental patient”typically refers to a person requiring the dental services of a dentalpractitioner, it also includes herein any person regarding whom it isdesired to create a 3D numerical model of the intra oral cavity thereof,for example for the purpose of practicing the same or for carrying outresearch.

The term “prosthesis” is herein taken to include any restoration orveneering, including any onlays, such as crowns and bridges, forexample, and inlays, such as caps, for example, and any other artificialpartial or complete denture.

While the term “preparation” typically refers to the stump (includingthe finish line and shoulder) that is left of the tooth that is to bereplaced by the prosthesis—typically a crown—and on which the crown isto be mounted, the term herein also includes artificial stumps, pivots,cores and posts, or other devices that may be implanted in the intraoralcavity in such a position or in a position that is optimal forimplanting the crown.

The term “prosthodontic procedure” refers, inter alia, to any procedureinvolving the intraoral cavity and directed to the design, manufactureor installation of a dental prosthesis at a dental site within theintraoral cavity, or a real or virtual model thereof, or directed to thedesign and preparation of the dental site to receive such a prosthesis.

The term “numerical entity” is used herein synonymously with virtualmodel and other such terms, and relates to a virtual representation of areal object, typically a dentition or at least a part of intraoralcavity, or of a real model thereof, for example.

The present invention, in a first aspect thereof, relates to a methodfor providing feedback data useful in at least one prosthodonticprocedure associated with the intra oral cavity, comprising:

(a) providing at least one numerical entity representative of thethree-dimensional surface geometry of at least part of the intra-oralcavity;

(b) manipulating said entity to provide desired data of a type useful inat least a first said procedure;

(c) determining at least one relationship between said desired data andsaid first procedure; and

(d) generating feedback data representative of said at least onerelationship.

Typically, in the said prosthodontic procedure, dental material has beenpreviously removed from said part of the intra-oral cavity by means of asecond procedure.

Optionally, step (c) comprises testing an adequacy of said desired datafor performing said first procedure according to at least onepredetermined parameter, and step (d) comprises generating feedback datarepresentative of said adequacy.

The method is typically directed at a said first procedure comprisingmounting at least one dental prosthesis with respect to a dentalpreparation comprised in said intraoral cavity and provided prior tostep (a).

In a first embodiment of the invention, said desired data relates to thegeometry of a finish line associated with said dental preparation. Step(c) comprises determining whether or not the said finish line geometryis suitable for receiving a prosthesis according to predeterminedparameters; said feedback data in step (d) comprises a suitable messageadvising whether or not said finish line geometry is suitable, accordingto said determination in step (c). In step (c) it may be determined thatthe said finish line geometry is not suitable for receiving a prosthesisaccording to predetermined parameters, and in such a case the method mayfurther comprise the step:

(e) providing suggested changes to said finish line geometry such as toprovide a new finish line geometry that is suitable for receiving aprosthesis according to predetermined parameters.

The suggested changes may be calculated according to predeterminedrules. Further, the suggested changes may be displayed on atwo-dimensional representation of said dental preparation, wherein saidnew finish line geometry is superimposed over said representation. Thelocation of said existing finish line geometry may be highlighted withrespect to said new finish line geometry.

The method may further comprise repeating steps (a) to (d) after furthermaterial has been removed from the preparation to conform a finish linethereof to said new finish line geometry.

The method may further comprise repeating steps (a) to (d) concurrentlywith each step of a material removal operation, said material removaloperation being adapted to conform a finish line of said preparation tosaid new finish line geometry, wherein step (e) is performed at eachstep of said material removal operation.

In a second embodiment, the desired data relates to an insertion pathgeometry for said prosthesis with respect to said dental preparation andsurrounding dental tissues. Step (c) comprises determining whether ornot the said insertion path geometry is suitable for enabling saidprosthesis to be mounted with respect to said dental preparation. Thefeedback data may comprise a suitable message advising whether or notsaid insertion path geometry is suitable, according to saiddetermination in step (c). In step (c) it may be determined that thesaid insertion path geometry is not suitable for receiving a prosthesisaccording to predetermined parameters, and the method may then furthercomprise the step:

(f) providing suggested changes to said dental preparation such as toprovide a new insertion path geometry that is suitable for receiving aprosthesis according to predetermined parameters.

The suggested changes may be determined on the basis of identifyingoverlapping areas between the prosthesis and the preparation, andproviding guidance as to corresponding changes required in at least oneof said prosthesis and said preparation. Further, the suggested changesmay be displayed on a two-dimensional representation of said dentalpreparation, wherein said new insertion path geometry is superimposedover said representation.

The method may further comprise repeating steps (a) to (d) after furthermaterial has been removed from the preparation to conform saidpreparation to said new insertion path geometry.

The method may further comprise repeating steps (a) to (d) concurrentlywith each step of a material removal operation, said material removaloperation being adapted to said preparation to said new insertion pathgeometry, wherein step (e) is evaluated at each step of said materialremoval operation.

The prosthesis in the second embodiment of the invention is typically acrown or bridge.

In a third embodiment of the invention, the desired data relates to atleast one predetermined dimension between said dental preparation andsaid prosthesis. Step (c) comprises determining whether or not the saidat least one dimension is suitable for enabling a prosthesis to bereceived according to predetermined parameters. The at least onedimension typically relates to a characteristic thickness of saidprosthesis. The said prosthesis may comprises a ceramic cap that ismountable over a metal coping bonded to said preparation, or a porcelainfused to metal (PFM) cap, for example.

The feedback data typically comprises a suitable message advisingwhether or not said at least one dimension is suitable, according tosaid determination in step (c). In step (c) it may be determined thatthe said at least one dimension is not suitable for receiving aprosthesis according to predetermined parameters, and further comprisesthe step:

(e) providing suggested changes to preparation geometry such as toprovide a dimension that is suitable for receiving a prosthesisaccording to predetermined parameters.

The suggested changes may be determined taking into consideration thetype of prosthesis to be implanted at said preparation. The suggestedchanges may be displayed on a two-dimensional representation of saiddental preparation, wherein said changes to preparation geometry aresuperimposed over said representation.

Optionally, the method may further comprise repeating steps (a) to (d)after further material has been removed from the preparation to conformsaid preparation to said new preparation geometry.

Optionally, the method may further comprise repeating steps (a) to (d)concurrently with each step of a material removal operation, saidmaterial removal operation being adapted to conform said preparation tosaid new preparation geometry, wherein step (e) is evaluated at eachstep of said material removal operation.

For all embodiments, step (a) is typically performed by scanning said atleast part of said intra oral cavity using a suitable 3D surfacescanner.

According to a second aspect of the invention, in step (c) saidrelationship may be insufficiently determined due to incompletedefinition of numerical entity provided by step (a). The method may thenfurther comprise the step of determining the location of at least onearea of said intra oral cavity where 3D definition thereof is requiredfor enabling step (c) to be performed. Said determination of thelocation of said at least one area may be performed by suitablealgorithms. The said at least one area is displayed on a two-dimensionalrepresentation of said dental preparation, wherein said at least onearea is superimposed over said representation.

The prosthesis typically comprises any one of an inlay, onlay, crown,bridge or restoration.

Optionally, step (b) comprises simulating said procedure first withrespect to said numerical entity to provide said desired data.

According to the second aspect of the invention, step (a) comprises thesteps of:

scanning a part of said intra-oral cavity to provide a 3D numericalentity thereof;

determining whether a definition of said 3D numerical entity issufficient for enabling step (c) to be performed;

if said definition is insufficient, advising a user to continue scanninga different part of said intra-oral cavity, and repeating step (ii)until said definition is sufficient, wherein step (v) is performed;

if said definition is sufficient in step (ii), proceeding with step (v);

advising a user that said definition is sufficient, and proceeding withsteps (b) to (d).

Optionally, in step (a), said numerical entity further comprises colordata of said part of the intra oral cavity, and step (b) comprisesdifferentiating parts of said entity according to whether the said colorassociated therewith is correlated with soft tissues or hard tissues ofthe intra oral cavity.

Optionally, step (a) may be performed in one location, and at least oneof steps (b) to (d) may be performed in at least one different location.

Optionally, step (d) is provided substantially in real-time with respectto step (a), or within a short time period thereof, typically in heorder of seconds or fractions of a second.

According to the second aspect of the invention, a method of providingfeedback data useful in at least one prosthodontic procedure associatedwith the intra oral cavity, comprises:

(i) providing at least one numerical entity representative of thethree-dimensional surface geometry of at least part of the intra-oralcavity that has been previously modified by means of a first part ofsaid procedure;

(ii) manipulating said entity to provide desired data useful in at leasta second part of said procedure;

(iii) testing adequacy of said desired data for performing said secondpart of said procedure; and

(iv) generating feedback data representative of said adequacy.

Typically, the first part of said procedure comprises a dental materialremoval operation in said intra-oral cavity. Further typically, step(ii) comprises manipulating said entity to determine sufficiency ofdefinition of said numerical entity in step (i) with respect to saidfirst said procedure, and providing sufficiency data representative ofsaid sufficiency, and step (iii) comprises determining at least onerelationship between said sufficiency data and said first procedure. Inone application of the method according to the second aspect of theinvention, the desired data may relates to a measure of surface datadefinition of said entity.

In the third aspect of the invention, the feedback data is essentiallyused in an interactive manner together with a material removing processto facilitate the performance of a procedure with respect to theintraoral cavity.

The present invention also relates to a system for providing feedbackdata useful in at least one prosthodontic procedure associated with theintra oral cavity comprising:

(A) scanner means for providing at least one numerical entityrepresentative of the three-dimensional surface geometry of at leastpart of the intra-oral cavity;

(B) microprocessor means for manipulating said entity to provide desireddata of a type useful in at least a first said procedure, and fordetermining at least one relationship between said desired data and saidfirst procedure; and

(C) output means for outputting feedback data representative of said atleast one relationship generated by said microprocessor means.

The scanner may comprises a confocal scanner, for example. Preferably,the scanner comprises a capability for providing color data as well asgeometrical data of a surface. Typically, the output means comprises avisual and/or audio display means. The microprocessor means is adaptedfor operation according to the method of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to understand the invention and to see how it may be carriedout in practice, a preferred embodiment will now be described, by way ofnon-limiting example only, with reference to the accompanying drawings,in which:

FIG. 1 is a block diagram illustrating steps of a method according tothe first aspect of the invention.

FIG. 2 is a block diagram illustrating elements of a system according tothe present invention.

FIG. 3 illustrates a numerical entity of the intraoral cavity obtainedwith the system of FIG. 2.

FIG. 4 illustrates a virtual crown prosthesis with respect to a virtualpreparation area.

FIG. 5 illustrates dimensional parameters associated with the crown ofFIG. 4.

FIG. 6 illustrates the insertion path for a crown prosthesis withrespect to a preparation.

FIG. 7 illustrates the insertion path for another crown prosthesis withrespect to a preparation, constrained to follow the insertion pathdefined by the internal surface of the prosthesis.

FIG. 8 illustrates the insertion path for the prosthesis of FIG. 7 withrespect to a preparation, constrained to follow the insertion pathdefined by the external surface of the prosthesis.

FIG. 9 illustrates an auxiliary prosthesis for use with the preparationstump having an undercut.

FIG. 10 illustrates a bridge prosthesis having a suitable the insertionpath with respect to a preparation.

FIG. 11 illustrates a bridge prosthesis having a non-suitable insertionpath for with respect to a preparation.

FIG. 12 is a block diagram illustrating steps of a method according tothe second aspect of the invention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 illustrates a method 10 for providing feedback data useful in atleast one prosthodontic procedure associated with the intra oral cavity,in accordance with a first aspect of the invention. The method comprisesthe following basic steps:

Step 11: providing at least one numerical entity representative of thethree-dimensional surface geometry of at least part of the intra-oralcavity from which dental material has been removed.

Step 12: manipulating said entity to provide desired data of a typeuseful in at least a first said procedure.

Step 13: determining at least one relationship between said desired dataand said first procedure.

Step 14: generating feedback data representative of said at least onerelationship.

Thus, in the first aspect of the invention, the feedback data isessentially used to facilitate the performance of a prosthodonticprocedure with respect to the intraoral cavity.

Preferably, steps 11 to 14 are carried out in a relatively short spaceof time, more preferably in real time or close thereto.

For all embodiments, the first step 11 of the method according to thepresent invention relates to providing at least one numerical entitythat is representative of the three-dimensional surface. The saidnumerical entity is typically at least “three-dimensional”, that is,each data point of the data set comprises at least three primeindependent variables relating to spatial coordinates of a surface,typically defined along orthogonal Cartesian axes, x, y, z.Alternatively, these variables may be defined along polar axes or anyother geometric system in which a surface may be described. Thus, thenumerical entity typically comprises a data set having a plurality of atleast 3-dimensional arrays—(x, y, z), wherein each array represents thex, y, z, geometrical coordinates.

Any suitable means may be used to provide the numerical entity. FIG. 2illustrates the main elements of the system 50 according to the presentinvention, comprising a suitable scanner 31, a microprocessor orcomputer 52, and a display means 54. According to the invention,digitised three-dimensional (3D) information W (FIG. 3) of the patient'sintra-oral cavity, or part thereof, is created by the system 50 usingscanner 31. Preferably, the 3D digitized data of the intraoral cavity isobtained, including the dentition and associated anatomical structuresof a patient. The scanning means 31 may include, for example, ahand-held scanner that is used by the practitioner or other user toacquire the 3D data. Advantageously, a probe for determining threedimensional structure by confocal focusing of an array of light beamsmay be used, for example as manufactured under the name of PROSTHOCAD oras disclosed in WO 00/08415, the contents of which are incorporatedherein in their entirety.

The system 50 is typically located at a dental clinic, and may be linkedto one or more service centers 23 and/or dental labs 26, via acommunication means or network such as for example the Internet or othersuitable communications medium such as an intranet, local accessnetwork, public switched telephone network, cable network, satellitecommunication system, and the like, indicated by the cloud at 24.Optionally, it is also possible for some dental labs 26 to be linked toeach other, via the same one or a different one of said communicationmedium, for example when such dental clinics or labs form part of acommon commercial entity. Further optionally, such interlinked dentallabs 26 may be further linked with other entities, for example a headclinic or head lab, comprising a centralized data base (not shown).

Typically, the design and manufacture of dental appliances for use inthe intraoral cavity may be eventually carried out at the dental lab 26or at the service centre 23, or alternatively one or both of theseactivities may be shared between the two; in each case the design andmanufacture are preferably based on the original 3D data of the oralcavity previously obtained. Thus, exchange of data between the system 50and the dental lab 26 and/or service center 23 may be useful in creatingan optimal geometry for a preparation being made in the intraoral cavitythat enables the best prosthesis to be designed therefor, for example.

The dental lab 26 typically comprises a laboratory, or a design ormanufacturing entity that may provide direct technical services to thedental clinic in which the system 50 is located. Such services mayinclude, for example, scanning, manufacturing, analyzing the preparationin the intra oral cavity to mark the location of the finish line, forexample, as disclosed in U.S. Ser. No. 10/623,707 and WO 04/008981, alsoassigned to the present assignee, and the contents of which areincorporated herein in their entirety, and so on. The dental lab 26 istypically characterized as being equipped or otherwise able to designpart or whole prostheses, and/or to partially manufacture or assemblethe same, particularly where close tolerances are relatively lesscritical. On the other hand, while the service center 23 is alsoequipped to design part or whole prostheses, and/or to fully orpartially manufacture and/or assemble the same, it is particularlysuited to do any of these activities where close or tight tolerances arein fact critical and/or difficult to achieve.

While the service centre 23 and dental labs 26 may be located in adifferent geographical zone to the dental clinic, for example, differentcountries, different cities in the same country, different neighborhoodsin the same city, or even different buildings in the same neighborhood,they may also be housed in the same building, and in any case maintaintheir separate functions and capabilities, as described herein.

The system 50 may also be linked to one or more consultation centers 27,also via network 24, wherein such consultation centers 27 may comprisedental experts, for example, that may provide feedback data to the userof system 50, based on data transmitted therefrom to the centers 27,according to the invention.

According to the present invention, step 11 is carried out after amaterial removal operation has been applied to a part of the intra oralcavity. Such a material removal operation may be executed using anysuitable machining tool that is adapted for material removal, and mayinclude inter alia mechanical tools such as drills for example, lasertools such as for example laser drills or cutters, ultrasonic tools suchas for example ultrasonic cutters, and so on. Alternatively oradditionally, the material removal operation may comprise a loss ofdental material, occurring, for example, via disease, mechanical forcessuch as a blow to the teeth for example, and so on.

Such a material removal operation may be directed for the purpose of, ormay require, prosthodontic procedures, and may include the constructionof a dental preparation at a dental site, so as to receive a prosthesissuch as a crown, for example, or for providing a dental filling orrestoration thereat.

Alternatively, the 3D digitized data may be obtained in any othersuitable manner, including other suitable intra oral scanningtechniques, based on optical methods, direct contact or any other means,applied directly to the patient's dentition. Alternatively, X-ray based,CT based, MRI based, or any other type of scanning of the patient'sintra-oral cavity may be used. The dimensional data may be associatedwith a complete dentition, or of a partial dentition, for example suchas a preparation only of the intra oral cavity.

Typically, the 3D digitized data is obtained in a manner such thatenables the data to be procured from the patient and analysed accordingto the invention during a regular visit of a patient to a practitioner.

Thus, advantageously, such a scanner 31 makes use of confocal imagingfor providing an accurate three-dimensional representation of the targetsurface within the intra-oral cavity.

Optionally, the numerical entity may further comprise a fourth primeindependent variable, relating to a color parameter that is expressednumerically and is associated with the spatial coordinates. The colorparameter may itself be comprised of independent prime colorvariables—for example relating to the red, blue and green (RGB)components associated with the color parameter. Alternatively, the colorparameter may be expressed in terms of the Hue, Saturation and Intensity(HIS). Alternatively, any other color parameter may be used, includingparameters that provide a measure of internal reflectance andtranslucency, or any other optical property of teeth. Thus, such anumerical entity typically comprises a data set having a plurality of4-dimensional arrays—(x, y, z, c), wherein each array represents the x,y, z, geometrical coordinates, and wherein c represents the color value,of a point on a surface within the intra-oral cavity. Any suitable meansmay be used to provide this numerical entity. For example, athree-dimensional surface scanner with color capabilities may be used.Thus, advantageously, such a scanner makes use of confocal imaging forproviding an accurate three-dimensional representation of the targetsurface within the intra-oral cavity. Color values may then added toeach data point of this data set by obtaining a two-dimensional colorimage of the target surface, and then mapping the color values of thetwo-dimensional image onto the three-dimensional “image”, for example asdescribed in co-pending applications assigned to the present assignee,U.S. Ser. No. 60/580,109, entitled “METHOD FOR PROVIDING DATA ASSOCIATEDWITH THE INTRAORAL CAVITY”, and U.S. Ser. No. 60/580,108, entitled“METHOD AND APPARATUS FOR COLOR IMAGING A THREE-DIMENSIONAL STRUCTURE”.These references are incorporated herein in their entirety by referencethereto.

While only a limited number of embodiments of the present inventionaccording to a first aspect are now described hereinbelow, it may beappreciated that the method of the invention may be used for a very widevariety of applications in which feedback data may be obtained for usein procedures associated with the oral cavity.

There are a number of exemplary procedures for which the method 10 is ofparticular utility. In one such example, the procedure relates to theprovision of a prosthesis, such as a crown or bridge, for example, andinlays, such as caps, for example, and any other artificial partial orcomplete denture. In each case, an area in the intra oral cavity needsto be prepared for receiving the crown, bridge and so on. In the case ofcrown prosthesis, one tooth site needs to be prepared, while for abridge prosthesis, two preparations need to be created, one at each ofthe abutment teeth for anchoring the bridge. Inlays require a differenttype of preparation at the tooth site.

Referring to FIG. 4, a virtual representation of such a crown, generallydesignated 100, has an internal surface 120 and lower edge 130 thatneeds to be very precisely defined and manufactured to match thepreparation 80 and finish line 84, respectively, in the intraoral cavity200 of a patient. If the crown 100 is to comprise a coping 160, the saidinternal surface 120 is that of the coping 160.

The crown 100, which may be formed from a plurality of layers,preferably needs to have a natural looking appearance. Further, thedimensions of the crown 100, in particular the definition of theexternal surface 140 depends on external factors and needs to be such asto enable the crown 100 to fit between the adjacent teeth A, B, and toprovide proper occlusion with the teeth D of the facing jaw (FIG. 3).

At the very least, the external surface 140 of the crown is such as toprovide certain critical linear dimensions that comply with at least oneof the target width or target height of a site or location on the jaw onwhich the crown is to be fitted. The target width may include themesiodistal size of a tooth that is being replaced by the crown 100, andmay be defined such as to provide adequate clearance between the crown100 and adjacent teeth A, B, when the crown 100 is fixed onto thecorresponding preparation in the intraoral cavity. The target height ofthe crown 100 may be defined such as to provide adequate occlusion withthe “working side” of the tooth and avoiding interfering contact betweenthe crown and teeth of the opposite jaw when the crown is fixed onto thecorresponding preparation 80 in the intraoral cavity.

An outer shape for the external surface 140 may be chosen in a number ofways. For example, if the original tooth that the crown 100 is replacingis still available, and the outer surface thereof is of a reasonableform, this original tooth may be scanned and the 3D data of the surfaceobtained. If necessary, this 3D data may be considered as a startingpoint, and the final shape of the external surface 140 is obtained bymanipulating this data as required by the technician or other user thatis designing the surface 140. Alternatively, if the patient has areasonably healthy tooth on the same jaw but on the adjacent quadrant ata position corresponding to where the crown is to be fitted, the 3D dataof the surface of this tooth is obtained. Optionally, this tooth may bescanned as described herein to obtain the 3D spatial coordinatesthereof, unless this data may already be available from the 3D data ofthe oral cavity 200 stored in the processor 52. Typically, such 3D-datawould need to be transformed to provide a lateral inversion of thecoordinates, suitable for a prosthesis in the other half of the jaw.Alternatively, a suitable profile for surface 140 may be chosen andobtained from a library 35 that comprises the 3D spatial profiles ofshapes or profiles of the outer surfaces of a plurality of crowns andteeth. If necessary the relative size and shape of the surface 140 maybe adjusted by the user to better match the other teeth in the jaw.Then, the chosen surface is adjusted in any suitable manner, eithermanually, automatically, interactively or in any other manner, in orderthat the required target dimensions of surface 140 will fit within acontrol volume that defines the maximum dimensions of the crown 100, asrequired to conform to the space available in the intra oral cavity 200.In particular, the control volume may be chosen such as to provideadequate clearance between the crown and adjacent teeth, and adequateocclusion with the opposite teeth, when the crown 100 is properly fixedonto the preparation.

The processor 52 also has suitable software to define the inner surface120 according to predetermined parameters. These parameters take intoaccount the geometries of the external surface of the preparation 80including finish line 84, the spacing required between the coping (ifone is to be used with the crown) or the internal surface of the crown(if no coping is used) and the preparation to accommodate the adhesiveor cement that is used to provide the bond between the two. Theprocessor 52 may also comprise suitable software to provide the externalshape of such a coping 160, and thus provide a complete geometricalrepresentation or 3D data of the coping 160, digitally. The externalsurface of the coping 160 may be defined in any number of ways.Typically, at least a majority of the external surface of the stump 82is displaced from the internal surface thereof by a uniform amount toprovide an approximately constant thickness throughout. However, thethickness of the coping 160 may vary for a number of reasons. Forexample, it may be necessary in some cases to provide a coping that isstronger in some parts than in others, reflecting the activity that thecrown 100 will be expected to engage in—as a molar, incisor, canine andso on.

The design of the external surface 140 and the internal surface 120 maybe executed by the processor 52 at the dental clinic, or alternativelyat the service center 23, or at the dental lab 26. If at the latter, andif use is made of a library of 3D spatial profiles of shapes or profilesof the outer surfaces of a plurality of crowns and teeth, then thedental lab 26 can make use of library of the service centre 23, viacommunications network 24. Similarly, if the design is carried out atthe dental clinic, the processor 52 may also make use of the library ofthe service centre 23, via communications network 24. Alternatively, thesystem 50 may have its own digital library 35 of 3D spatial profiles ofshapes or profiles of the outer surfaces of a plurality of crowns andteeth, operatively connected to a processor 52 or other computer, asillustrated in FIG. 2, which comprises display 54 and user interface 59such as a mouse and/or keyboard.

Referring to FIG. 4, in a first embodiment of the invention, the method10 is adapted for providing feedback data regarding the definition ofthe finish line 84. In particular, it is desired to receive suchfeedback data referring to the quality and clearness of the finish line84, and optionally including the shoulder 85.

The finish line 84 may be of any type thereof, for example knife edge,feather edge, chamfer, chamfer bevel, shoulder, shoulder bevel, and soon. Alternatively, the finish line 84 may comprise a combination ofdifferent types around the periphery of the preparation, for examplepart of the finish line for a particular preparation may be knife edge,while another part may be feather edge.

Thus, having scanned the intraoral cavity 200, in particular the targetzone T including the preparation 80, finish line 84 and (whereappropriate) shoulder 85, the processor 52 then manipulates theresulting numerical entity W to identify the finish line 84. This may bedone using any suitable algorithm. For this purpose, it may beadvantageous for the entity W to also include color components for eachsurface point defined therein. The differentiation of dental surfacecolor between the hard tissues and the soft tissues may be helpful inautomatically defining the finish line, as described in the aforesaidco-pending application entitled “METHOD FOR PROVIDING DATA ASSOCIATEDWITH THE INTRAORAL CAVITY”. Generally, the shoulder type (e.g.,porcelain shoulder, metal collar and so on) should match and be suitablefor the prosthesis it is desired to implant at the dental site.

The geometry of the finish line 84 and optionally shoulder 85 may thenbe analysed by the processor 52 according to predetermined rules, toestablish the relationship between the virtual finish line thusidentified, and the function which the finish line 84 and optionallyshoulder 85 is to play in the mounting of the prosthesis to thepreparation. Such rules may comprise, for example one or more of thefollowing:—

(a) the finish line is continuous about the full periphery of thepreparation;

(b) the thickness of the shoulder 85, i.e., the radial dimension betweenthe edge of the finish line 84 and the preparation 80, lies within apredetermined range;

(c) the thickness of the shoulder 85 is substantially uniform along theperiphery thereof;

(d) there are no abrupt changes in slope of the finish line 84 along theperiphery thereof;

(e) the type of prosthesis to be implanted.

It may then be established by the processor 52 whether the finish line84 and/or shoulder 85 comply with such rules, and can then providefeedback data to the user. Such feedback data may take many differentforms. For example, in the positive, i.e., that the finish line, forexample, is adequate, the processor 52 may be adapted to transmit asignal via display 54. Such a signal may be an audio or visual signal,such as for example the sound of a bell 51 of a particular frequency ora colored light source 53 such as a green light, which may light up andremain lit, or may blink, or the signal may be more complex, such as forexample a message on a screen stating that the finish line is suitable.

In the negative, i.e., in cases where the finish line is not suitableaccording to the aforesaid rules, for example, the feedback data mayfirst advise where the finish line is deficient. For example, ifreferring to the first rule listed above, there is a step ordiscontinuity along the periphery of the finish line, the location andextent of the same may be alerted to the user. For this purpose, a 3Drepresentation of the preparation site may be displayed, with the partof the finish line in question highlighted in a different color to therest of the finish line and/or of the preparation and so on. Similarly,if the practitioner is attempting to create a feather edge finish line(and this desire should be first inputted to the system 50 in anappropriate manner), deviations in geometry from this type of finishline—for example, part of the finish line is chamfered—may also bealerted to the user, for example by suitably annotating a graphicalimage of the preparation with colors and so on.

This also enables the practitioner to check whether the finish line isof the type he/she wants, or at least how close it is to this ideal.

Further, the feed back data may also comprise indications to the user asto where to modify the finish line 84 or shoulder 85 to achieve betterresults. In this context, an image of the numerical entity may bedisplayed in the display 54, with the finish line 84 and optionally alsothe shoulder 85 highlighted thereon. Then, the zones of the finish linethat require further work may be contrasted with respect to the finishline 84 and/or the shoulder 85, for example by coloring such zones in adifferent color to the rest of the image. Optionally, zones may becolored differently according to the type of work required. For example,zones deficient with respect to rule (a) above may be colored in red,while those deficient with respect to rule (b) are colored in blue, andso on.

Thus, suggested changes to the finish line may be displayed on atwo-dimensional representation of said dental preparation, via display54, wherein said new finish line geometry may be superimposed over saidrepresentation.

Modification of the finish line 84 and/or shoulder 85 typically requiresa material removing operation, and after doing so, the intra oral cavity200 may be re-scanned to provide a second numerical entity. The secondnumerical entity, in particular the portions thereof relating to thefinish line 84 or shoulder 85, may then be analysed as before todetermine whether the finish line 84 or shoulder 85 are acceptableaccording to the predetermined rules, and without reference to theoriginal entity W. Alternatively, the second numerical entity may becompared with the original entity W, and any deviations between the twoentities may be highlighted in display 54 in order to facilitate thenext cycle of modification to the finish line.

Alternatively, the processor 52 may simply display the numerical entityand the highlighted finish line 84 and/or shoulder 85 on display 54, andthis may at times represent sufficient feedback data for enabling theuser to inspect the image thus created and to determine in a subjectivemanner whether the finish line and/or the shoulder are suitable or not.In all cases, the processor 52 is suitably programmed to enable thenumerical entities to be viewed at any suitable angle and /ormagnification.

Optionally, the numerical entity W may be transmitted to one or moreremote locations, such as for example a service center of dental lab 26,to be analysed there by a computer (not shown), or by a skilledtechnician or another user. The computer or skilled technician at thedental lab 26 may then communicate the results of the analysis to theoriginal user via the communication network 24, or a differentcommunication network, for example via cellular phone. These results maybe in the form of numerical information that may be displayed, forexample, or verbal instructions on how to proceed.

In a second embodiment of the invention, the method 10 is adapted forproviding feedback data regarding the suitability of the preparation toaccept a prosthesis of a predetermined type. Alternatively, the method10 according to this embodiment is adapted for providing feed back dataregarding the type of prosthesis that may be suitable for use with thepreparation 80. In particular, it is desired to receive such feedbackdata referring to at least one predetermined dimension, such as forexample a characteristic thickness of a prosthesis with respect to thegeometry of the preparation and the adjacent teeth A and B.

Thus, having scanned the intraoral cavity 200, in particular the targetzone including the preparation 80 and adjacent teeth A and B, asdescribed above, mutatis mutandis, the processor 52 then manipulates theresulting numerical entity W to identify the external surface 125 of thestump 82 of preparation 80 (FIG. 4). This may be done, for example, byfirst identifying the finish line and optionally shoulder, for exampleas described above, and then isolating the coping surface enclosed bythe perimeter defined by the finish line and/or shoulder. Then, anexternal crown surface 140 is chosen or designed for the crown, such asto fit properly in the space between the adjacent teeth A, B, asdescribed hereinbefore. Then the relationship between the externalsurface 125 (which is typically closely correlated to the internalsurface 120 of the crown 100) or of the internal surface 120, and theexternal surface 140 may then be analysed by the processor 52 accordingto predetermined rules. This serves to establish the relationshipbetween the thickness (referred to collectively herein as t) of thewalls of crown 100, and the material from which the real crown (based onsuch a virtual crown 100) is to be produced as a function of theexternal surface 140 of the stump. Typically, such a relationship isdependent on the material from which the real crown is to be made.Referring to FIG. 5, such rules may comprise, for example one or more ofthe following:—

the occlusal-gingival thickness t₁ between the apex 121 of the outersurface 125 (or of the inner surface 120) and the apex 141 of the crown100;

the mesial-distal thicknesses t₂, t₄, between the outer surface 125 (orof the inner surface 120) and the external surface 140 of the crown 100at various occlusal-gingival distances;

the labial-lingual thickness t₃ t₅, between the outer surface 125 (or ofthe inner surface 120) and the external surface 140 of the crown 100 atvarious occlusal-gingival distances. The suitability of the stump 82itself may also be analysed by suitable rules, to determine, forexample, if it has sufficient mechanical strength to support the crownor other prosthesis thereon. For example, the volume of the stump and/orother critical thicknesses thereof may be determined by the processor52. In another example, the stump may be analysed to determine whetherhere are any discontinuities or undercuts that would provide insertionpath problems, and these may be highlighted and brought to the attentionof the user.

It may then be established by the processor 52 whether the geometry ofthe stump 82 complies with such rules, and can then provide suitablefeedback data to the user. Such feedback data may take many differentforms. For example, in the positive, i.e., that the stump 82 isadequate, the processor may be adapted to send a corresponding signal todisplay 54. Such a signal may be an audio or visual signal, such as forexample the sound of a bell of a particular frequency or a colored lightsuch as a green light, which may light up and remain lit, or may blink,or the signal may be more complex, such as a message on a screen statingthat the finish line is suitable. Of course such a signal should bedifferent from that provided with respect to the first embodimentdescribed above, when both are available to the user.

In the negative, i.e., in cases where the stump 82 is not suitableaccording to the aforesaid rules, for example, the feed back data maycomprise indications to the user as follows:—

To advise the user as to where to modify the stump 82 to achieve betterresults. In this context, an image of the numerical entity W may bedisplayed in the display 54, with the stump highlighted thereon. Then,the zones of the stump that require further work may be contrasted withrespect to the stump 82, for example by coloring such zones in adifferent color. Optionally, zones may be colored differently accordingto the type of work required. For example, zones deficient with respectto rule (a) above may be colored in red, while those deficient withrespect to rule (b) are colored in blue, and so on.

To advise the user that the stump 82, as is, provides a crown thicknessthat is too thick, and that therefore a filing composition needs to beadded at least to some portions of the stump. The display 54 can thenshow where to add the composition, and when this is done, the intra oralcavity 200 may be rescanned to determine haw and where to modify thestump. Alternatively, if the stump 84 is totally unsuitable theprocessor 52 provides a suitable signal to be displayed by display 54,and it may be necessary to replace the stump 84 with a pivot, core orpost.

To advise the user that although the stump is unsuitable for use with aprosthesis made from one material (pre-defined), it may be suitable ifthe stump is made from a different material. For example, a stump madefrom PFM (Porcelaim Fused Metal) can be thinner than a whole ceramiccrown. Therefore, if a PFM crown was originally decided upon, it may beadvisable to switch to a whole ceramic crown, and the processor 52 candetermine whether the stump 82 would be suitable for such a crown.

Optionally, a contour or occlusion map of the target zone T may beprovided, for example as disclosed in U.S. Pat. No. 6,334,853 and EP0984739, the contents of which are incorporated in their entiretyherein, and which references are also assigned to the present assignee.Such a dental occlusion map is indicative of distances between oppositeregions on facing surfaces of opposite dental surfaces of the upper jawsof the mouth, for example the preparation 80 and the opposed tooth D.The occlusion map may be created by manipulating the entity W so as todetermine the distances between opposite regions on the opposite dentalsurfaces of the upper and lower jaws of the target zone T, and thensetting up a correspondence between the determined distances and regionson a mapping surface. Accordingly, it is possible to provide, forexample, a colored contour map showing the occlusion distances withrespect to the preparation 80, for example, and from this determinewhether and what parts of the preparation require further work, orwhether there is preparation adequacy or preparation clearance regardingthe worked target zone T. In particular, the occlusion map may informthe practitioner whether the preparation is adequate for the type ofcrown that he/she was intending to use, or what type of crown may beused, if any, with the preparation in its present condition. Forexample, a PFM crown typically requires greater occlusion between thepreparation and opposed tooth (due the requirement for greater materialthickness) than an all-ceramic crown, which in turn needs more clearancethan a metal crown.

Optionally, the system 50 may be configured for automatically advisingwhether, for a given desired type of prosthesis (for example ceramic,PFM, metal and so on) the preparation is adequate, or conversely, giventhe current state of the preparation, what is the optimal type ofprosthesis that is best suited for it, or if in fact the preparation isstill unsuitable for receiving any prosthesis in its current state. Thisfeature allows the practitioner to check whether the preparation is ofthe type that he/she wants. Further, the system 50 may be adapted toprovide the practitioner with indications on how to further work thepreparation so that it is optimally suited to the type of prosthesisthat it is desired to be used therewith. For example, the contour mapand/or a graphical representation of the target zone T may be annotated,for example by suitably coloring corresponding areas therein, toindicate the corresponding areas of the preparation where more materialneeds to be removed, for example, fo as to accommodate a particular typeof prosthesis.

Modification of the stump 82 typically requires a material removingoperation, and after doing so, the intra oral cavity may be re-scannedto provide a second numerical entity. The second numerical entity, inparticular the portions thereof relating to the stump 82, may then beanalysed as before to determine whether the geometry of the stump 82 isacceptable according to the predetermined rules, and without referenceto the original entity. Alternatively, such a second numerical entitymay be compared with the original entity, and any deviations between thetwo may be highlighted in display 54 in order to facilitate the nextcycle of modification to the stump 82.

Alternatively, the processor 52 may simply display the numerical entityand the highlighted stump 82 on display 54, and this may at timesrepresent sufficient feedback for enabling the user to inspect the imagethus created and to determine in a subjective manner whether the stump82 is suitable or not.

Optionally, the numerical entity may be transmitted to a remote locationsuch as for example a dental lab 26, to be analysed there by a computer(not shown), or by a skilled technician or another user. The computer orskilled technician may then communicate the results of the analysis tothe original user via the communication network 24 to provide feedbackdata to the original user regarding the stump 82.

In a third embodiment, the method 10 is adapted for providing the userwith feed back data regarding the insertion path with respect to apreparation or preparations that is/are being created at a dental sitefor receiving a prosthesis such as a crown or bridge.

Taking the relatively simpler case of a crown first, the method 10comprises the first step of providing a numerical entity of theintraoral cavity, including in particular the part of the cavitycomprising the preparation. Optionally, and preferably, the numericalentity also comprises 3D data of the teeth A, B adjacent to thepreparation 80. The 3D numerical entity may be provided in a similarmanner to that described herein, mutatis mutandis.

In the next step, it is desired to determine whether the preparation issuitable to receive a crown prosthesis. One aspect of such adetermination is to advise the user whether the preparation 80 providesan adequate insertion path for the crown. In this connection, theprocessor 52 first identifies from the entity W the external surface 125corresponding to the part of the preparation onto which the crown is tobe mounted (FIG. 4), and suitable algorithms for this purpose may becreated, possibly as described above for the second embodiment, mutatismutandis. Then, a virtual model 100 of the crown is either created bythe processor 52, or input thereto by the user or a third party such asservice center or dental clinic 26, for example. Alternatively, thisprocess may be commenced with a virtual model of the coping 160. Thecrown model 100 must be sized such as to fit between the adjacent teethA, B, and thus be in abutting contact therewith when properly mountedonto the preparation 80. The crown model 100 may be a full 3D model,comprising an external 3D surface, or may simply comprise keydimensional parameters, such as for example the mesiodistal width of thetooth between the adjacent teeth A, B. The crown model 100 alsocomprises a full 3D representation of the internal 3D surface 125, whichmay ge substantially complementary to the external surface 120 of thepreparation, optionally taking into account an adhesive layer thicknessthat is to be introduced between the preparation and the said internalsurface. The processor 52 then calculates the insertion path for theinternal surface 120 of the virtual crown 100, and then checks whetherthis path is also suitable for the external surface 140 of the virtualcrown 100. Alternatively, the processor 52 calculates the insertion pathfor the external surface 140 of the virtual crown 100, and then checkswhether this path is also suitable for the internal surface 120 of thevirtual crown 100. Ideally, the insertion path of the virtual crown 100as a whole should enable the same to be maneuvered into position withrespect to the preparation without colliding with or unduly interferingwith other dental surfaces at or in the vicinity of the preparation.

For example, referring to FIG. 6, the geometry of the preparation 82approximates a right frustro-conical cone, and the central axis 101thereof is more or less perpendicular to the occlusal plane OP. In thisexample, the insertion path IP₁ of the internal surface constrains theexternal surface 140 to path IP₂, which enables the external surface ofthe virtual crown 100 to be guided to the mounted position on thepreparation without interfering or colliding with other parts of thedentition. In the Example illustrated in FIG. 7, the geometry of thepreparation is approximately that of a slanting frustro-convex cone,wherein the central axis 101 thereof is at a minimum angle α to theocclusal plane. In this example, the insertion path IP₁′ of the internalsurface constrains the external surface to path IP₂′, which would resultin the external surface 140 of the virtual crown 100 colliding withadjacent tooth B, and it would be impossible to fit a real crowncorresponding to the virtual crown 100 with such a preparation geometry.Similarly, in the example illustrated in FIG. 8, the insertion path IP₂″of the external surface constrains the internal surface to path IP₁″,which would result in an undercut part 105 of the virtual crown 100colliding with the stump 82, and it would be impossible to fit a realcrown corresponding to the virtual crown 100 with such a preparationgeometry. Optionally, the overhanging portion 88 and/or undercut part105 may be highlighted by suitably coloring the corresponding zone in agraphical representation of the target zone T.

Optionally, and particularly when the geometry of the preparation issimilar to that shown in FIG. 8, another type of plan may be consideredin place of or in conjunction with a material removal plan. Having aslanting frusto-conical profile for the preparation typically requiresmaterial to be removed until a substantial part of the overhangingportion 88 of the stump 82 is removed. Such a procedure may result inover-weakening of the stump 82. Instead, and according to the invention,it is possible to create an internal surface of the virtual crown 100that is not fully correlated to the external surface 125 of the stump82, but only partially correlated thereto, along areas thereof that arenon-overlapping in the direction of the insertion path, e.g., in whichthere is no undercuts. However, regarding the overlapping areas of thestump 82, i.e., the part of the stump overshadowed by the overhangingportion 88 in the direction of the insertion path, it is insteadpossible to create a portion of the internal surface. 120 of the crown100 corresponding thereto that is designed not to interfere or in anyway collide with the overlapping areas of the stump 82 when the same isinstalled via the appropriate insertion path. The overlapping areas orzones refer to portions of the crown 100 which would need to be removedto prevent collision of the internal surface 120 of the crown 100 withthe stump 82. However, this would leave a substantial cavity between thepart of the preparation and the corresponding part of the internalsurface of the crown. This cavity is preferably filled by manufacturingan auxiliary prosthesis 121 having the shape of this cavity, and thenbonding the auxiliary prosthesis to the stump 82, as illustrated in FIG.9. Alternatively, suitable cement or filler material may be bonded tothe overlapping areas, and these areas then subjected to a materialremoval operation to provide the desired result. Particularly in such acase, but also for the previous case in which an auxiliary prosthesisfor the cavity is bonded in place, the modified stump may be scanned tocheck the new geometry of the modified preparation.

The insertion paths for prostheses are preferably substantiallyrectilinear, to ease the user's task in duplicating the path whenmaneuvering the real crown onto the preparation. However, it is alsopossible to calculate insertion paths in which there is one or morechange in the direction thereof, and/or in which the crown (i.e., firstthe virtual crown, and then the real crown) can be rotated about one ormore of three orthogonal axes.

In some cases, there may be a plurality of possible insertion paths forthe internal surface, or particularly for the external surface, and theprocessor 52 can attempt to match such paths.

When more than one matching pair of internal and external insertionpaths match, the various alternatives may be presented to the user bymeans of display 54. Additionally or alternatively, the processor 52 maydetermine which matching pair is optimal, based on rules, or may presentthe different options in ascending or descending order of preference,according to any predetermined criteria, such as for example requiring aminimum number of direction or rotational changes in the path.

Preferably, display 54 displays an image of the dental site 200,together with the predicted insertion path of the internal surface andthat of the external surface constrained thereby, or vice versa, and theprocessor 52 also provides the necessary input to the display 54 tohighlight any part of the adjacent teeth A, B and/or preparation 80 thatinterfere with the particular insertion path. Alternatively, oradditionally, when a situation such as those illustrated in FIGS. 7, 8arises, the processor 52 may generate a suitable warning signal, audioand/or visual, warning the user that the insertion path for the currentpreparation geometry is not suitable, and that remedial action isrequired.

In particular, the processor may be programmed to determine possibleplans for removing additional dental material from the preparation 80 toenable a suitable insertion path to be provided. This may beaccomplished in a number of ways. For example, the processor maydetermine a particular suitable path for the external surface 140 of thevirtual crown 100, for example the simplest and most direct path, andthen identify the zones of the preparation which would need to beremoved to prevent collision of the internal surface of the crowntherewith, herein referred to as the “overlapping zones”. However, sincethe internal surface of the crown is a function of the external geometryof the preparation, this procedure is preferably accomplished in areiterative manner. That is, once the processor 52 identifies theoverlapping zones, and removes, in a virtual manner, a small part of theoverlapping zone. The amount of removal may be preset by the user, andany increment is possible. Preferably, such an amount may be correlatedto the minimum removal of material that is normally possible in ananalogous real life situation. The processor 52 then adjusts thegeometry of the internal surface of the virtual crown 100 to take intoaccount the new preparation geometry, and examines the insertion path ofthe inner surface with respect to the new preparation geometry. If thereis still interference between the internal surface and the preparation,more material is removed in the virtual sense, the geometry of theinternal surface 120 adjusted, and the new internal surface insertionpath re-examined for collision. Additional cycles may be performed untilthe external surface 125 of the preparation is suitably modified to becompatible with the insertion path.

In some cases, the result of such a virtual procedure may not beacceptable for a real crown, for example too much material needs to beremoved, and this would provide a much weakened stump 82, according topre-known rules.

Accordingly, the virtual procedure may be repeated, each time startingwith a different insertion path for the external surface 140, until areasonable preparation geometry is arrived at that is compatible withthe external insertion path and that is also reasonable according tosuch rules.

Additionally or alternatively, other virtual procedures for modifyingthe geometry of the preparation may be accomplished. For example, such aprocedure may involve a combination of reducing the overhanging portion,and adding an auxiliary prosthesis 121.

However, it may be possible, that, given the condition of thepreparation and the topology of the adjacent dental surfaces, noreasonable modified preparation geometry can be found. Such an outcomeis also feed back data that is presented to the user.

Thus, the geometry of such a preparation is optionally, and preferably,analysed according to such rules, and a suitable warning provided to theuser when the geometry of preparation is inherently unsuitable. Thewarning may be audio/and or visual, and may be simple, such as a bip orseries of bips, or a flashing light or lights, or may be complex forexample an audio or a visual message, created by the processor 52,actually describing the reason for the warning. For example, such awarning could comprise an audio and/or visual message stating “Warning!The stump geometry is defective!”. Where such warnings are audio, thedisplay 54 preferably comprises optional ear phone or headphones thatenable the user to hear the message, but not the patient, since such amessage may cause unnecessary alarm or anxiety to the patient. Suchearphones or headphones may be operatively connected to the processor 52via suitable cables, or via remote link such as an infraredtransmitter/receiver system, or may be integrated into display 54, forexample. A similar analysis and warning, where necessary, may beprovided at the beginning of the exercise, and thus alert the user thatthe original preparation is unsuitable, preferably listing the reasons.In either case, where the present or virtually modified preparation isinherently unsuitable, the processor 52 may be programmed to providerecommendations, such as to remove the preparation completely, and toreplace it with a pivot core or post.

On the other hand, if the processor 52 determines one or more materialremoval plans for the preparation 80 which theoretically yield areasonable preparation geometry compatible with a possible insertionpath, the different plans may be displayed to the user, who can thechoose one plan. Preferably, each plan comprises displaying theoverlapping areas of the preparation that require to be modified, andthe nature of the insertion path that is required for maneuvering theprosthesis into place. Both factors need to be weighed by the userbefore deciding how to proceed. The aforementioned overlapping areas canbe displayed over an image of the dentition (provided from the 3D entityW), and preferably such an image can be manipulated, for example on ascreen, to enable the user to fully study the plan.

Once a preparation modification plan is chosen, the user can modify thereal preparation area in the intraoral cavity as closely as possible tothe overlapping areas marked in the virtual model (3D numerical entity).At any point in the material removal procedure, the user may re-scan theintraoral cavity to check on the progress. For this purpose, theprocessor 52 may be further programmed to effectively overlay the newnumerical entity over the original entity, in particular to highlightthe differences in geometry between the areas in which actual materialremoval has occurred and the overlapping areas which were earmarked bythe procedure for material removal. Further, the processor 52 may befurther programmed to detect with respect to these entities wherematerial still needs to be removed, and where too much material has beenremoved. This may be displayed in display 54 on an image of theintraoral cavity, and the under-modified areas may be displayed in onecolor, say green, and then over modified areas may be displayed in adifferent color, say red. Preferably, should the presence ofover-modified areas be detected, i.e., areas where too much material hasbeen removed, the processor 52 recalculates the insertion path andadvises the user whether the original modification plan is stillpossible, or whether the excess material removal requires a modificationof the plan. Such a modification in the plan may be determined in asimilar manner to the original plan, as described above, mutatismutandis. Of course, it is also possible that the over modified areashave now rendered the preparation unsuitable according to theaforementioned rules, and the preparation must be replaced with anartificial pivot, core or post.

The methodology described above for an insertion path has been describedwith respect to a crown that is directly bonded onto a preparation, suchas for example a metallic crown. For other types of crowns (for exampleceramic crowns) that require a coping, the method is modified to takeaccount of the coping geometry. Thus, the external surface 125 of thestump is displaced outwardly to create a virtual representation of aconstant thickness coping. Alternatively, any other suitable means maybe used to define the coping external surface. The internal surface 120of the crown is then defined with respect to the external surface of thecoping, and is typically complementary thereto, optionally taking intoaccount a thin layer of adhesive.

The above method may also be adapted for the purpose of providing asuitable insertion path for the coping itself, mutatis mutandis.

The methodology described above for the insertion path of a crown may beused, mutatis mutandis, for any dental restoration or dental prosthesis.In the case of a bridge, in particular, preparations have to be createdin the abutment teeth on either side of the missing tooth, and thegeometries of both preparations need to be considered simultaneously inrelation to the insertion path of the bridge as a unit. Thus, referringto FIG. 10, the preparation geometries illustrated allow the bridge 150to be mounted via an insertion path 151, while the preparationgeometries illustrated in FIG. 11 do not provide a common insertion pathfor the bridge 150′. Thus, in order for the insertion path for thebridge 150 to be suitable, the individual insertion paths for the twopreparations must be parallel, and moreover, such an insertion path mustbe such as to avoid collision of the bridge with the adjacent teeth A′and B′. In the analysis and design. of modification plans for suchcases, the processor 52 may provide one or more plans for themodification of one or both of the preparations, substantially asdescribed above for a crown, mutatis mutandis. While the casesillustrated in FIGS. 10 and 11 relate to a 3-unit bridge, the aforegoingrelates, mutatis mutandis, to a multiple unit bridge as well.

The FIG. 12 illustrates a method 10′ for providing feedback data usefulin at least one prosthodontic procedure associated with the intra oralcavity, in accordance with a second aspect of the invention. In thesecond aspect of the invention, the method is concerned with ensuringthat numerical entity W sufficiently defines the area of interest of theintraoral cavity. The method 10′ comprises the following basic steps:

Step 11′: providing at least one numerical entity representative of thethree-dimensional surface geometry of at least part of the intra-oralcavity from which dental material has been removed.

Step 12′: manipulating said entity to determine sufficiency ofdefinition of said numerical entity in step 11′ with respect to a firstsaid procedure, and providing sufficiency data representative of saidsufficiency.

Step 13′: determining at least one relationship between said sufficiencydata and said first procedure.

Step 14′: generating feedback data representative of said at least onerelationship.

Preferably, steps 11′ to 14′ are carried out in a relatively short spaceof time, more preferably in real time or close thereto.

For all embodiments, the first step 11′ of the method according to thepresent invention relates to providing at least one numerical entitythat is representative of the three-dimensional surface. This step iscarried in a similar manner to step 11 of FIG. 1, as described above,mutatis mutandis.

Thus in step 11′, scanner 32 of system 50 (FIG. 2) scans the area ofinterest of the intraoral cavity and a numerical entity corresponding tothe surface scanned is created by processor 52 and optionally displayedby display 54. As with the first aspect of the invention, the data fromthe scanner may be transmitted to a dental clinic 23, service centre 26,or consultancy centre 27, inter alia, for creation of the numericalentity, which is then transmitted to the processor 52.

In step 12′, the processor 52 (or indeed another computer in theaforesaid dental clinic 23, service centre 26, or consultancy centre 27,inter alia) analyses the numerical entity to determine the sufficiencyof definition of the numerical entity. The numerical entity may beobtained in a single scan, or alternatively, the numerical entity isoriginally created by taking multiple scans of the target area, andstitching the numerical entities thus obtained together. In any case,the processor 52 first checks whether the numerical entity lacks surfacedata in any particular part thereof. Such a lack of data may be due tothe user not passing the scanner over the full zone to be scanned, forexample, or by taking multiple scan in wich there is insufficientoverlap, for example.

When multiple scan are employed, then, in step 11′, the scanner 31 maybe used for obtaining high resolution numerical sub-entitiesrepresentative of the surface topography within the intra-oral cavity.Accordingly, different zones of the intraoral cavity are sequentiallyscanned with scanner 31 to provide the corresponding sub entities. Someof these zones typically partially overlap with all the other zones,while other zones may only overlap with one or two other zones, and thustheoretically the corresponding sub-entities should have a portion oftheir data identical to one another within the overlap zone. However,since the scanner itself moves in orientation and position from scan toscan, the coordinates relating to these overlap zones will usually varybetween adjacent scans, even though they relate to the same spatialfeature. Nevertheless, by identifying the overlap zone within theentities, the spatial relationship between the entities may beestablished, and the various entities stitched together or combined toform a global numerical entity that comprises the full geometry andcolor representation of the target zone. The larger the overlap zone,the greater the accuracy with which the different zones may besynchronized or stitched together spatially. Where the sub entitiesinclude color data of the intraoral cavity 200, the actual stitchingtechnique may applied to data points corresponding to the hard tissuestherein, which have a different color to the soft tissues such as gums,for example as described in the aforesaid co-pending applicationentitled “METHOD FOR PROVIDING DATA ASSOCIATED WITH THE INTRAORALCAVITY”.

The zones that are scanned should preferably together fully span thetarget zone T of interest, however it sometimes happens that a part ofthe target zone is missed out, and thus after the stitching procedure iscompleted, the global numerical entity thus formed still lacks surfacedata in some areas. According to the invention, such areas areidentified in steps 12′ and 13′ by the processor 52 which determinesthat the density of data points in some parts of the entity is below apredetermined value, indicative of a lack of data thereat, for example.

Additionally or alternatively, having provided to the processor 52 thetype of procedure for which the numerical entity is required, theprocessor can analyse the numerical entity in a different manner todetermine whether it is sufficiently defined for this purpose. Forexample, having found quantitatively there is sufficient data, it is nownecessary to determine if qualitatively the data is sufficient.

For example, if the numerical entity is to be used in the context of acrown prosthesis, for example as described above for the first aspect ofthe invention, it is important for the finish line to be well defined.Sometimes, parts of the finish line may be defined on a dental surfacethat is close to orthogonal with respect to the occlusal plane. If aconfocal-type scanner is used at 31 for providing the surface data forthis part of finish line, it is possible for the accuracy of definitionof the finish line to be diminished the closer to parallel the outputface of the scanner is with respect to the occlusal plane. Greateraccuracy could be obtained in the scanner is turned to face theaforesaid dental surface close to face-on rather than close to edge-on.Accordingly, the processor 52 may determine whether the definition ofthe finish line is sufficiently good, and this may be done by comparingthe orientation of the scanner 32 with respect to the aforesaid dentalsurface, according to preset criteria, for example. Thus, in step 13′,the processor 52 determines whether data is missing, or whether theaccuracy of the data of the numerical entity is insufficient.

In step 14′, feedback data is generated to alert the user as to how tocorrect for the insufficiency of definition. For example, in the casewhere some surface areas of the entity are missing, the processor 52first identifies the missing areas for the user, and then may computethe best angle and position for the scanner 31 to scan the intraoralcavity such as to provide the missing surface data. This information maybe provided by display 54, for example by providing a graphical image ofthe entity, with the deficient areas marked hereon, and then arrows ormarkers with respect thereto showing the desired position of the scanner31. Of course, it may be that more than one scan is required to make upfor the missing data, and the processor provides the required feedbackdata to deal with each scan.

Similarly, in the case where some surface areas of the entity requirebetter definition, the processor 52 may compute the best angle andposition for the scanner 31 to scan the intraoral cavity such as toprovide better definition of those areas. This information may also beprovided by display 54, for example by providing a graphical image ofthe entity, and then arrows or markers with respect thereto showing thedesired position of the scanner 31. As before, more than one scan may berequired to provide the higher accuracy data, and the processor providesthe required feedback data to deal with each scan. Other parts requiringspecial definition may include, for example, undercut zones of thepreparation.

Furthermore, the processor may be programmed to alert the user when theentity is sufficiently well defined for the purpose for which it isneeded. In such a case, the feedback data is deigned to alert the userthat the scan is complete, and may comprise a distinct visual or audiosignal, similar but distinguishable from other audio/visual signalsprovided by display 54, as described herein, mutatis mutandis.

It should be noted that the method 10′ according to the second aspect ofthe invention may be carried out in step 11 (FIG. 1) of the first aspectof the invention, such as to ensure that the entity provided in step 11is sufficient for steps 12 to 14 thereof.

Thus, in the second aspect of the invention, the feedback data mayessentially be used to facilitate the acquisition of data that may beused to construct the numerical entity for subsequent use, for exampleaccording to the first aspect of the invention.

According to the first and second aspects of the invention, the entityobtained by scanning via scanner 31 is displayed in real time viadisplay 54, and when the scanning is complete and acceptable, feedbackdata is provided alerting the user to this fact.

Further, the present invention, according to the first and secondaspects thereof, may be used solely to obtain verification that aparticular preparation is in a suitable condition for implanting aprosthesis.

Further, the analysis of the scanned data, whether locally or at aremote site such as for example the service centers 23, dental labs 26,and so on, typically via suitable algorithms, may also use the followingparameters: the type of restoration required; patient parameters—age,sex, origin, dental condition (implants in the scanned area, rootcanals, soft tissue condition, and so on), budget for the procedure, andso on.

In the third aspect of the invention, the feedback data is essentiallyused in an interactive manner together with a material removing processto facilitate the performance of a procedure with respect to theintraoral cavity.

For example, the process for removing dental material to create thepreparation may be effected in a number of stages, at the end of eachmaterial removing stage the preparation area being scanned and displayedin real time to guide the dental practitioner as to how to proceed tothe next stage, such as to provide an optimal preparation geometry. Inparticular, when the prosthesis is a bridge, the system guides thepractitioner to provide the one of the preparation zones, and then basedon this geometry calculates an optimal geometry for the secondpreparation zone required for the bridge, and correspondingly guides thepractitioner accordingly. At each material removing stage, the processor52 re-evaluates the full picture, and may suggest that the firstpreparation be modified instead of or in addition to the secondpreparation.

At least the first aspect of the invention may be used with respect to apositive model of a dentition, in a similar manner to that describedabove for a real dentition, mutatis mutandis.

While the method of the invention has been described, based on arepresentation of surface information, the three dimensional entities inthe oral cavity, such as for example the teeth gums and so on, and alsothe 3D entities that are created by the system 50, including thepreparation 10, for example, may be described instead by solidrepresentations or any other topographical or geometricalrepresentations.

According to the invention feedback data useful in prosthodonticprocedures associated with the intra oral cavity is provided. First, a3D numerical model of the target zone in the intra oral cavity isprovided, and this is manipulated so as to extract particular data thatmay be useful in a particular procedure, for example data relating tothe finish line or to the shape and size of a preparation. Therelationship between this data and the procedure is then determined, forexample the clearance between the preparation and the intended crown.Feedback data, indicative of this relationship, is then generated, forexample whether the preparation geometry is adequate for the particulartype of prosthesis.

In the method claims that follow, alphabetic characters and Romannumerals used to designate claim steps are provided for convenience onlyand do not imply any particular order of performing the steps.

Finally, it should be noted that the word “comprising” as usedthroughout the appended claims is to be interpreted to mean “includingbut not limited to”.

While there has been shown and disclosed exemplary embodiments inaccordance with the invention, it will be appreciated that many changesmay be made therein without departing from the spirit of the invention.

1. A method for providing feedback data useful in at least oneprosthodontic procedure associated with the intra oral cavity,comprising: (a) providing at least one numerical entity representativeof the three-dimensional surface geometry of at least part of theintra-oral cavity; (b) manipulating said entity to provide desired dataof a type useful in at least a first said procedure; (c) determining atleast one relationship between said desired data and said firstprocedure; and (d) generating feedback data representative of said atleast one relationship.
 2. Method according to claim 1, wherein dentalmaterial has been previously removed from said part of the intra-oralcavity by means of a second procedure.
 3. Method according to claim 1,wherein step (c) comprises testing an adequacy of said desired data forperforming said first procedure according to at least one predeterminedparameter.
 4. Method according to claim 3, wherein step (d) comprisesgenerating feedback data representative of said adequacy.
 5. Methodaccording to claim 3, wherein said first procedure comprises mounting atleast one dental prosthesis with respect to a dental preparationcomprised in said intraoral cavity and provided prior to step (a). 6.Method according to claim 5, wherein said desired data relates to thegeometry of a finish line associated with said dental preparation. 7.Method according to claim 6, wherein step (c) comprises determiningwhether or not the said finish line geometry is suitable for receiving aprosthesis according to predetermined parameters.
 8. Method according toclaim 7, wherein said feedback data in step (d) comprises a suitablemessage advising whether or not said finish line geometry is suitable,according to said determination in step (c).
 9. Method according toclaim 7, wherein in step (c) it is determined that the said finish linegeometry is not suitable for receiving a prosthesis according topredetermined parameters, and further comprises the step: (e) providingsuggested changes to said finish line geometry such as to provide a newfinish line geometry that is suitable for receiving a prosthesisaccording to predetermined parameters.
 10. Method according to claim 9,wherein said suggested changes are calculated according to predeterminedrules.
 11. Method according to claim 9, wherein said suggested changesare displayed on a two-dimensional representation of said dentalpreparation, wherein said new finish line geometry is superimposed oversaid representation.
 12. Method according to claim 11, wherein alocation of said existing finish line geometry is highlighted withrespect to said new finish line geometry.
 13. Method according to claim9, further comprising repeating steps (a) to (d) after further materialhas been removed from the preparation to conform a finish line thereofto said new finish line geometry.
 14. Method according to claim 9,further comprising repeating steps (a) to (d) concurrently with eachstep of a material removal operation, said material removal operationbeing adapted to conform a finish line of said preparation to said newfinish line geometry, wherein step (e) is performed at each step of saidmaterial removal operation.
 15. Method according to claim 5, whereinsaid desired data relates to an insertion path geometry for saidprosthesis with respect to said dental preparation and surroundingdental tissues.
 16. Method according to claim 15, wherein step (c)comprises determining whether or not the said insertion path geometry issuitable for enabling said prosthesis to be mounted with respect to saiddental preparation.
 17. Method according to claim 16, wherein saidfeedback data comprises a suitable message advising whether or not saidinsertion path geometry is suitable, according to said determination instep (c).
 18. Method according to claim 16, wherein in step (c) it isdetermined that the said insertion path geometry is not suitable forreceiving a prosthesis according to predetermined parameters, andfurther comprises the step: (f) providing suggested changes to saiddental preparation such as to provide a new insertion path geometry thatis suitable for receiving a prosthesis according to predeterminedparameters.
 19. Method according to claim 18, wherein said suggestedchanges are determined on the basis of identifying overlapping areasbetween the prosthesis and the preparation, and providing guidance as tocorresponding changes required in at least one of said prosthesis andsaid preparation.
 20. Method according to claim 18, wherein saidsuggested changes are displayed on a two-dimensional representation ofsaid dental preparation, wherein said new insertion path geometry issuperimposed over said representation.
 21. Method according to claim 18,further comprising repeating steps (a) to (d) after further material hasbeen removed from the preparation to conform said preparation to saidnew insertion path geometry.
 22. Method according to claim 18, furthercomprising repeating steps (a) to (d) concurrently with each step of amaterial removal operation, said material removal operation beingadapted to said preparation to said new insertion path geometry, whereinstep (e) is evaluated at each step of said material removal operation.23. Method according to claim 15, wherein said prosthesis is any one ofa crown or bridge.
 24. Method according to claim 5, wherein said desireddata relates to at least one predetermined dimension between said dentalpreparation and said prosthesis.
 25. Method according to claim 24,wherein step (c) comprises determining whether or not the said at leastone dimension is suitable for enabling a prosthesis to be receivedaccording to predetermined parameters.
 26. Method according to claim 25wherein said at least one dimension relates to a characteristicthickness of said prosthesis.
 27. Method according to claim 25, whereinsaid prosthesis comprises a ceramic cap that is mountable over a metalcoping bonded to said preparation.
 28. Method according to claim 25,wherein said prosthesis comprises a porcelain fused to metal (PFM) cap.29. Method according to claim 25, wherein said feedback data comprises asuitable message advising whether or not said at least one dimension issuitable, according to said determination in step (c).
 30. Methodaccording to claim 25, wherein in step (c) it is determined that thesaid at least one dimension is not suitable for receiving a prosthesisaccording to predetermined parameters, and further comprises the step:(e) providing suggested changes to preparation geometry such as toprovide a dimension that is suitable for receiving a prosthesisaccording to predetermined parameters.
 31. Method according to claim 30,wherein said suggested changes are determined taking into considerationthe type of prosthesis to be implanted at said preparation.
 32. Methodaccording to claim 30, wherein said suggested changes are displayed on atwo-dimensional representation of said dental preparation, wherein saidchanges to preparation geometry are superimposed over saidrepresentation.
 33. Method according to claim 30, further comprisingrepeating steps (a) to (d) after further material has been removed fromthe preparation to conform said preparation to said new preparationgeometry.
 34. Method according to claim 30, further comprising repeatingsteps (a) to (d) concurrently with each step of a material removaloperation, said material removal operation being adapted to conform saidpreparation to said new preparation geometry, wherein step (e) isevaluated at each step of said material removal operation.
 35. Methodaccording to claim 1, wherein step (a) is performed by scanning said atleast part of said intra oral cavity using a suitable 3D surfacescanner.
 36. Method according to claim 35, wherein in step (c) saidrelationship is insufficiently determined due to incomplete definitionof numerical entity provided by step (a).
 37. Method according to claim36, further comprising the step of determining the location of at leastone area of said intra oral cavity where 3D definition thereof isrequired for enabling step (c) to be performed.
 38. Method according toclaim 37, wherein said determination of the location of said at leastone area is performed by suitable algorithms.
 39. Method according toclaim 37, wherein said at least one area is displayed on atwo-dimensional representation of said dental preparation, wherein saidat least one area is superimposed over said representation.
 40. Methodaccording to claim 5 wherein said prosthesis comprises any one of aninlay onlay, crown, bridge or restoration.
 41. Method according to claim1, wherein step (b) comprises simulating said procedure first withrespect to said numerical entity to provide said desired data. 42.Method according to claim 1, wherein step (a) comprises the steps of:(i) scanning a part of said intra-oral cavity to provide a 3D numericalentity thereof; (ii) determining whether a definition of said 3Dnumerical entity is sufficient for enabling step (c) to be performed;(iii) if said definition is insufficient, advising a user to continuescanning a different part of said intra-oral cavity, and repeating step(ii) until said definition is sufficient, wherein step (v) is performed;(iv) if said definition is sufficient in step (ii), proceeding with step(v); (v) advising a user that said definition is sufficient, andproceeding with steps (b) to (d).
 43. Method according to claim 1,wherein in step (a), said numerical entity further comprises color dataof said part of the intra oral cavity.
 44. Method according to claim 43,wherein step (b) comprises differentiating parts of said entityaccording to whether the said color associated therewith is correlatedwith soft tissues or hard tissues of the intra oral cavity.
 45. Methodas claimed in claim 1, wherein step (a) is performed in one location,and at least one of steps (b) to (d) are performed in at least onedifferent location.
 46. Method according to claim 1, wherein step (d) isprovided substantially in real-time with respect to step (a).
 47. Methodof providing feedback data useful in at least one prosthodonticprocedure associated with the intra oral cavity, comprising: (i)providing at least one numerical entity representative of thethree-dimensional surface geometry of at least part of the intra-oralcavity that has been previously modified by means of a first part ofsaid procedure; (ii) manipulating said entity to provide desired datauseful in at least a second part of said procedure; (iii) testingadequacy of said desired data for performing said second part of saidprocedure; and (iv) generating feedback data representative of saidadequacy.
 48. Method according to claim 47, wherein said first part ofsaid procedure comprises a dental material removal operation in saidintra-oral cavity.
 49. Method according to claim 47, wherein step (ii)comprises manipulating said entity to determine sufficiency ofdefinition of said numerical entity in step (i) with respect to saidfirst said procedure, and providing sufficiency data representative ofsaid sufficiency, and wherein step (iii) comprises determining at leastone relationship between said sufficiency data and said first procedure.50. Method according to claim 47, wherein said desired data relates to ameasure of surface data definition of said entity.
 51. System forproviding feedback data useful in at least one prosthodontic procedureassociated with the intra oral cavity comprising: (A) scanner means forproviding at least one numerical entity representative of thethree-dimensional surface geometry of at least part of the intra-oralcavity; (B) microprocessor means adapted for manipulating said entity toprovide desired data of a type useful in at least a first saidprocedure, and for determining at least one relationship between saiddesired data and said first procedure; and (C) output means foroutputting feedback data representative of said at least onerelationship generated by said microprocessor means.
 52. Systemaccording to claim 51, wherein said scanner comprises a confocalscanner.
 53. System according to clam 52, wherein said scanner comprisesa capability for providing color data as well as geometrical data of asurface.
 54. System according to claim 51, wherein said output meanscomprises a visual and/or audio display means.
 55. System according toclaim 51, wherein said microprocessor means is adapted for operationaccording to a method as defined in any one of claims 1 to 50.